Social ageing: exploring the drivers of late-life changes in social behaviour in mammals

Abstract

Social interactions help group-living organisms cope with socio-environmental challenges and are central to survival and reproductive success. Recent research has shown that social behaviour and relationships can change across the lifespan, a phenomenon referred to as ‘social ageing’. Given the importance of social integration for health and well-being, age-dependent changes in social behaviour can modulate how fitness changes with age and may be an important source of unexplained variation in individual patterns of senescence. However, integrating social behaviour into ageing research requires a deeper understanding of the causes and consequences of age-based changes in social behaviour. Here, we provide an overview of the drivers of late-life changes in sociality. We suggest that explanations for social ageing can be categorized into three groups: changes in sociality that (a) occur as a result of senescence; (b) result from adaptations to ameliorate the negative effects of senescence; and/or (c) result from positive effects of age and demographic changes. Quantifying the relative contribution of these processes to late-life changes in sociality will allow us to move towards a more holistic understanding of how and why these patterns emerge and will provide important insights into the potential for social ageing to delay or accelerate other patterns of senescence.

Within-individual changes reveal increasing social selectivity with age in rhesus macaques

“…Similar to these studies, our findings indicate that female rhesus macaques demonstrate patterns of social aging that resemble the human social aging phenotype, suggesting that social selectivity may not solely arise from an awareness of limited time but may also be underpinned by other biological pathways. Many mammals face increased constraints and limitations as they age, including physiological changes as well as physical, energetic, and cognitive declines that might limit the capacity for, or alter the costs and benefits of, social interaction (16). Being more selective in partner choice and focusing on important or preferred partners with age might therefore reflect an adaptive response to these constraints.…”

“…Conclusively demonstrating that declines in sociality result from active selectivity with age remains challenging, and not only due to a lack of longitudinal data. Similar declines in sociality with age might occur as physical or mental deterioration inhibits an individual’s ability to interact with others or leads to reduced desirability of older individuals as social partners (16). Previous research has worked to disentangle these alternative hypotheses by showing, for instance, that Barbary macaques maintain an interest in vocal and visual social stimuli in later life (11, 46).…”

“…In other cases, older individuals have been shown to engage in fewer energy-demanding activities (4, 46) or exhibit changes in space use with age (47) which invites the possibility that decreases in affiliation are not adaptive, but instead a direct consequence of deteriorating physical condition. Alternatively, social connectedness might be less strongly selected for at older ages, or declines in sociality could occur because enhanced social experience and skill among aged individuals free them from reliance on social capital to successfully navigate their environment (16). Previous research in this system has shown that the fitness benefits of social affiliation are stronger in prime-age females than in old-age females (26), in support of these possibilities.…”

“…This makes it important to rule out alternative explanations for age-based reductions in sociality. For example, declines in social engagement might be driven by loss of social interest, motivation, or physical ability to engage (16). Alternatively, older individuals might be perceived as less valuable partners (e.g.…”

Ageing in a collective: The impact of ageing individuals on social network structure

“…Using both empirical data and a theoretical model, we explore how social ageing of individuals relates to measures of indirect connectedness and overall network structure in a group-living primate, the rhesus macaque (Macaca mulatta), which is an emerging model in social ageing research [36,50]. Rhesus macaques are highly social cercopithecine primates that live in matrilineal kin-groups and exhibit clearly differentiated social relationships with kinbiased affiliation [51][52][53].…”